The broad, long-term objective of this project is the development of a non-invasive optical technique for imaging blood flow in human skin with high spatial resolution. Optical Doppler Tomography (ODT) combines Doppler velocimetry with optical coherence tomography (OCT) to measure blood flow velocity at discrete user-specified locations in highly scattering biological tissues. The exceptionally high resolution of ODT allows noninvasive imaging of both in vivo blood microcirculation and tissue structures surrounding the vessel. Our central hypothesis in this research proposal is that ODT provides a practical methodology for characterization of port wine stain (PWS) birthmarks, prior to institution of laser therapy. To this end, we propose four specific aims: (1) an ODT system based on spectral interferometry will be designed and constructed; (2) an imaging construction algorithm will be developed; (3) a series of experiments to image in vivo blood flow will be carried out using the high speed ODT system to confirm image accuracy and fidelity; and (4) demonstrate in clinical studies how ODT can assist in the clinical management of PWS patients receiving laser therapy. In preliminary studies conducted on in vitro turbid samples, in vivo model vasculatures and in situ PWS human skin, the feasibility and potential application of ODT to characterize and image blood flow with high spatial resolution at discrete user-specified locations in highly scattering biological tissues such as human skin has been demonstrated. The objective of the studies proposed herein is to extend these initial findings and is expected to lead to the development of a new technology for the clinical management of PWS patients.